Modern elevators utilize sophisticated software in controllers which control most aspects of the elevator's operation. The controllers gather information from various sources in the elevator system and use that information to efficiently operate the elevator. Thus elevator speed, starting, stopping, dispatching, floor positioning or leveling, and the like are all governed by the controller. In performing its functions, a most important input for the controller software is the speed and location of the car. Modern elevators generally use tapes secured to the car and journaled in the machine room and pit which move about pulleys as the car ascends and descends in the hoistway. The tapes are monitored by a sensor to detect car speed and position.
In view of the efficiency and accuracy of modern software-controlled elevators, there is a substantial demand for modernization of older elevators so that they can also be controlled and operated by appropriate software. In order to accomplish this modernization, the selector assembly on the older elevators must be replaced with a sensing device which can interact with the new controller microprocessor. One solution to the problem of replacing the prior art selector assemblies is to connect a sensor or monitor to the shaft of the electric motor which drives the traction sheave on the elevator. The monitor of choice is an encoder which measures motor shaft revolutions and translates the results into machine readable signals delivered to the controller microprocessor. The encoder operates by having a rotatable encoder shaft connected to the motor shaft so as to rotate conjointly therewith. The number, direction, and speed of encoder shaft rotations thus indicates the direction of movement, speed and position of the elevator car. Use of the encoders to monitor motor shaft rotation requires very accurate alignment of the axes of the encoder shaft and the motor shaft. Misalignment of these shafts often results in damaged couplings, and in damage to the encoder bearings which are relatively delicate. Poor car motion control can also occur with shaft misalignment.
Improved alignment can be accomplished through tight tolerances on the ports using pilot surfaces of the existing motor shaft O.D. and motor shaft beam housing I.D. This solution, however, can be expensive, and requires great care in installation. Springy flexible collar-type couplings can be attached to the ends of the respective shafts to provide some margin for coaxial misalignment, however, their annular shape limits their utility in combating damage or shortened useful life in cases of shaft misalignment.